Reaction rates & equilibrium

Effect of concentration on rate of reaction

• Increase in conc = increase in number of particles in the same volume

• Particles closer together & vibrate more frequently

• More frequent collisions & increased rate of reaction

Effect of catalyst on rate of reaction

• Provides alternate reaction pathway by lowering activation energy

• Increases rate of reaction without undergoing any permanent change itself

2 types of catalysts

• Homogenous

• Heterogeneous

Homogenous catalysts

• Catalyst that has the same physical state as the reactants

• React together to form an intermediate

• Breaks down to give products & regenerates the catalyst

2 examples of homogenous catalysts

• H2SO4

• Cl radical

Heterogenous catalyst

• Catalyst with a different physical state as reactants

• Reactants are adsorbed on surface of catalyst

• Products released through desorption

2 examples of heterogenous catalysts

• Fe (s)

• Ni (s)

Benefits of catalysts to increase sustainability

• Using catalysts for industrial reactions means less activation energy & less energy & fossil fuels used

• So reducing CO2 emissions - environmentally sustainable

• Also cuts costs & increases profitability

• So economically sustainable

Describe Boltzmann distribution

• X-axis = energy

• Y-axis = number of molecules within a given energy

Explain effect of temperature on rate of reaction using Boltzmann distribution

• At higher temperature - high KE - more molecules have energy greater than / equal to activation energy

• Greater proportion of successful frequent collisions

• Increased rate of reaction

Explain effect of catalyst on rate of reaction using Boltzmann distribution

• Catalyst provides alternative route with lower activation energy

• Greater proportion of molecules have energy equal to / greater than the activation energy

• More successful frequent collisions, increased rate of reaction

Dynamic equilibrium

• Exists in a closed system

• Rate of forward reaction is equal to the rate of the reverse reaction

• Concentrations of reactants and products don’t change

Effect of change in temperature on equilibrium position

• Increase in temperature = shift to endothermic side

• Decrease in temperature = shift to exothermic side

Effect of change in concentration on equilibrium position

• Increase in concentration of reactants = shifts to right

• Increase in concentration of products = shifts to left

Effect of change in pressure on equilibrium position

• Increase in pressure = shifts to the side with fewest moles

• Decrease in pressure = shifts to side with most moles

Effect of catalyst on equilibrium position

• No change - rate of forward & reverse reaction sped up equally

• Increases rate of attainment, no effect on yield

Calculating equilibrium constant

Kc = [C]^c x [D]^d / [A]^a x [B]^b

Meaning of square brackets

Concentration of the substance in the brackets

Meanings of values of Kc

• Kc = 1 = position of equilibrium is halfway between reactants and products

• Kc < 1 = position of equilibrium is towards the reactants

• Kc > 1 = position of equilibrium is towards the products